1. Field of the Invention
The present invention relates to network communication, and in particular relates to a network switch.
2. Description of the Related Art
Quality of service (QOS) is a defined level of performance in a data communications system. When data is broken into packets that travel through the same switches or routers in a LAN or WAN with all other data, QoS mechanisms are one method of ensuring quality by giving some data priority over other data. These switches and routers can make the actual determination of which packet has priority with the mechanisms in the network software. The software mechanisms can be based on a real time property of a packet or class of services that are assigned to users based on company policies. For example, IP telephony packets may require higher priority to prevent jitter and delay. The packet priority can also be determined on the basis of service level agreements contracted between a company and users according to the expense the user is charged.
The conventional method checks a specific field of the packet header to determine packet priority. For example, the “type of service” field in the IP header of a packet can be set by a packet sender to notify switches or routers of the data priority. A “user priority” field in the VLAN tag header for IEEE 802.1q is available, and the user priority field can be used to store a priority level of the frame.
However, if those fields in the packet header are the only reference to decide packet priority in a switch or router, the actual packet priority may be misinterpreted or disguised. For example, assume there are two users A and B connecting to the internet backbone via a network switch of an Internet service provider (ISP). If user B is charged higher than user A by the ISP, the network switch should process packets sent from user B at higher priority than packets from user A. However, if user A continues sending packets with a higher value in the “user priority” field than packets from user B, the network switch will process packets from user A with precedence over packets from user B, decreasing profits of the ISP's. Thus, a method for implementing a varying grades of QOS in a network switch is desirable.